Two narrow slits are illuminated by a laser with a wavelength of 582 nm. The int

Question

Two narrow slits are illuminated by a laser with a wavelength of 582 nm. The interference pattern on a screen located x = 5.30 m away shows that the third-order bright fringe is located y = 8.10 cm away from the central bright fringe. Calculate the distance between the two slits. First you have to calculate the angle of the maximum. Then you can use the formula for bright fringes of double slits. The screen is now moved 1.4 m further away. What is the new distance between the central and the third-order bright fringe?

Explanation / Answer

In interfreence or diffraction pattern

the needed equation is Y = mLR/d---------------1

and d sin theta = mL--------------------2

where L = wavelgnth

m = order = 1,2,3,4, ......... for brigth bands

m = 1.5, 2.5, 3.5, 4.5, ......for dark bands

R is the distance from slit to screen

Y = disatnce from central spot to nth order fringe or fringe width

so here now we apply

d = m L R /Y

d = 3 * 582 e-9* 5.3/0.081

d = 1.143 e -4 m
--------------------------------------------------------------

for max theta = 90

then use d sin theta = m L

m = 1.143 e-4 / 582 e -9

m = 197   

--------------------------------------------------
New R = 1.4 + 5.3 = 6.7 m

ao

Y = 3 * 582 e -9 * 6.7/(1.143 e -4)

Y 10.2 cm

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